This invention relates to generating particle beams and measuring and regulating their characteristics, specifically using a Faraday cup or a plurality of Faraday cups.
As is well known, particle beams can be used for a variety of applications. One such application is ion implantation where beams of ion are generated and directed toward workpieces to implant ions into the workpieces. The workpieces can be wafers or other target substrates. The beams of ions can have large cross-section, that is, larger than or equal to about 1 cm.sup.2, preferably larger than or equal to about 7 cm.sup.2. Such beams of ion can be employed in conjunction with scanning arrangements to produce deposit of ions over wide areas. The scanning arrangements may be implemented to perform magnetic scanning of the beams in one direction and mechanical scanning of the workpieces in another direction.
During an ion implantation process, it is generally desirable to implant the ions uniformly across the workpiece. This uniformity of the implantation process depends on the ion beam having the same characteristics in its entire scan region and during the entire implantation process. However, an ion beam can have different characteristics in different points of the scan and at different times during the ion implantation process. Therefore, to ensure uniform implantation, the characteristics of the ion beam need to be monitored and the parameters affecting its characteristics need to be adjusted accordingly. Additionally, in some applications, it is desirable to change the ion beam characteristics to implant ions according to a new set of requirements and characteristics. For example, it may be desirable to increase or decrease the ion beam current for a new set of workpieces. In that case, it can be more efficient and less expensive to change the ion beam characteristics "on the fly," that is without stopping the implantation process to, for example, reconfigure the measuring instruments for the new ion beam.
The uniformity of the ion implantation process can be characterized by the value of an implantation dose delivered to the entire workpiece and also by the uniformity of the dose across the wafer. Implantation dose (D) may be defined as the number of ions delivered to a workpiece per unit of area. Since the value of the delivered dose depends on the value of the ion beam current, one method of monitoring and regulating the dose is to monitor the ion beam current by using Faraday cups. Once the dose is determined, the parameters governing the implantation process can be adjusted to compensate for variations in beam uniformity. Such parameters can include the speed of mechanical scanning of the workpiece and the parameters governing the ion beam current.